When we had the "man in white" controversy, I always thought the team should have given white shirts to everyone in that section the next game and had them make all kinds of weird movements and signs out there.
Uhhh, so the right time to check is when the game doesn't matter and there's no obvious black mark on the brim of the hat?
https://www.mlb.com/news/giovanny-gallegos-hat-taken-by-umpires-in-cardinals-win